Sehwag, Gambhir, Dhoni, Yuvraj, Raina, Irfan Pathan etc. were not noobs or inexperienced in 2007. We've already seen how Pant did when he was introduced in T20I even though that is the ideal format for him.
These players should be playing one-day and 4-day cricket. They're not going to develop playing T20s where they'll be playing against bigger men capable of clearing the boundaries more easily. There's already enough of T20 for them between the IPL and Syed Mushtaq Ali T20 Trophy. Keep the T20Is for the 'national and A' team, not U19.